Noise Attenuation Through Optimised Acoustic Metamaterials: A Low Form Factor Design for Targeted Noise Reduction

The need for state-of-the-art noise silencers with minimal form factor is increasing along with the requirements for high performance cooling systems in commercial settings. Acoustic metamaterials (AMMs) have the potential for exceptional performance with unprecedented noise reduction capabilities. In this paper, a low form factor AMM is designed from an interlinked network of resonators, composed of cubes with spherical cavities connected via cylindrical channels on each face of the cube. The target frequency performance of the design is achieved through optimisation based on Nelder-Mead algorithm within the COMSOL ® Multiphysics optimisation module, and is performed in an FEM simulation framework. The obtained geometrical parameters, namely, radius of cylinder (
$R_{c}$
), length of cylinder (
$L_{c}$
), radius of sphere (
$R_{s}$
) and also the number of cells,
$n$
, are such that a targeted incident noise frequency of 4100 Hz from a cooling fan is attenuated by the system, while also achieving minimal thickness. The optimised acoustic system is additively manufactured, and subsequently validated experimentally. Numerical simulation shows absorptivity of over 80 % with ≈ 8 mm thickness of the AMM. Experimental results are achieved from an induct application of the metamaterial. The AMM samples produce a reduction of over 3 dB in the far field of the duct exit.